Visualization of protein-RNA interactions in cytoplasmic polyhedrosis virus

Unlike the multiple-shelled organization of other Reoviridae members, cytop lasmic polyhedrosis virus (CPV) has a single-shelled capsid. The three-dime nsional structures of full and empty CPV by electron cryomicroscopy show id entical outer shells but differ inside. The outer surface reveals a T=1 ico sahedral shell decorated with spikes at its icosahedral vertices. The inter nal space of the empty CPV is unoccupied except for 12 mushroom-shaped dens ities attributed to the transcriptional enzyme complexes. The ordered doubl e-stranded RNA inside the full capsid forms spherical shells spaced 25 Angs trom apart. The RNA-protein interactions suggest a mechanism for RNA transc ription and release.